Kopano-Server does not start

I just wanted to “migrate” move from Zarafa to Kopano. My setup splits servers between Samba AD, MTA (sendmail) and Kopano. I am quite familiar with Zarafa but new to Kopano, although most thinks looks quite similar ;-)

AD and MTA are working. Mysql (MariaDB) works as well, access rights set and tested. However, the clean setup (have not taken over any data yet) Kopano-server service does not start up with the following loglevel 6 error message say:

The documentation refers to the release packages of Kopano and not the nightly community builds. For subscription holders Debian 9 is indeed not yet supported, but we aim to introduce support with the next mayor release (8.4).